Encrypted voice and data communication systems are well known in the art. These cryptosystems allow a user to digitally transmit information to one or more system users without it being intercepted and interpreted. This is accomplished by encrypting and decrypting the transmitted information with what is known as an encryption key. Encryption keys may be secret keys, where a single key is utilized for encryption and decryption, or public keys, where two or more keys are used.
Cryptosystems which utilize secret keys and public keys are well known in the art. Each type of cryptosystem provides some degree of privacy and authentication for digital communications. Secret-key cryptosystems utilize the traditional method known as symmetric key cryptography. In a symmetric key cryptosystem, a single electronic key is used both to encrypt and decrypt the transmitted information. Since only one key is used, the sender must provide the receiver with the key by some form of secure communication. The lack of a secure channel, which is usually why encryption is used in the first place, makes this system mostly obsolete in common practice these days.
Public-key cryptosystems, also referred to as asymmetric cryptosystems, provide another means of encrypting information. Such cryptosystems differ from secret-key cryptosystems in that two or more keys are required as opposed to one. In a public-key cryptosystem, each entity has a private key and a public key. Public keys are generally held in databases run by "Key Certificate Authorities" and are publicly known. However, each user's private key is known only by that user. Once a sender encrypts a message with a recipient's public key, it can only be decrypted using that recipient's private key. Because the computational power required to break a key increases exponentially with the length of key, longer keys provide greater security.
Private keys are usually between 512 and 4096 bits long, far too long for the average person to commit to memory. For this reason, most users of a public key cryptosystem store their private key on a personal computer or other personal device. The problem with this practice is that private key may be lost if the computer software crashes or computer hardware fails. In most cases, the user may have not "backed up" their data. This situation occurs more often than is convenient. In the event that the user wrote down the private key in a "safe" place and then lost it, the result is the same.
If or when this private key is lost or stolen, and thus compromised, a complicated "Key Revocation" process occurs. The user must perform the embarrassing task of informing all other users with whom he or she communicates with that the public/private key pair is no longer valid, and provide them with a new public key to use instead.
Another major drawback with current public key cryptosystems is that the users must have their private key with them to read any of their messages. This becomes a problem when the user is traveling and the private key is stored on their personal computer at home. In the current age of "roaming email" and other roaming communication, the technology is readily available for users to check their messages almost anywhere in the world. If the users do not have their private key with them, they cannot retrieve their messages. If the users do carry their private key with them while traveling, there is the risk that the private key may be lost or stolen. Furthermore, it is not always easy or convenient for users to carry around a piece of digital data with them that quickly integrates with other digital hardware worldwide.